From 54acfa91222787ae9170f94ddf8ee94192d1a1a5 Mon Sep 17 00:00:00 2001
From: Akihiko Odaki <nekomanma@pixiv.co.jp>
Date: Thu, 20 Jun 2019 18:37:42 +0900
Subject: [PATCH] [XamlC] Do not try to set a value to bound source property if
 unavailable (#6564)

---
 Xamarin.Forms.Build.Tasks/SetPropertiesVisitor.cs     | 19 ++++++++++++++++++-
 Xamarin.Forms.Xaml.UnitTests/BindingsCompiler.xaml    |  1 +
 Xamarin.Forms.Xaml.UnitTests/BindingsCompiler.xaml.cs |  6 ++++++
 3 files changed, 25 insertions(+), 1 deletion(-)

diff --git a/Xamarin.Forms.Build.Tasks/SetPropertiesVisitor.cs b/Xamarin.Forms.Build.Tasks/SetPropertiesVisitor.cs
index 3c49d2f..d63cf8d 100644
--- a/Xamarin.Forms.Build.Tasks/SetPropertiesVisitor.cs
+++ b/Xamarin.Forms.Build.Tasks/SetPropertiesVisitor.cs
@@ -665,7 +665,13 @@ namespace Xamarin.Forms.Build.Tasks
 			else
 				il.Emit(Ldarg_0);
 			var locs = new Dictionary<TypeReference, VariableDefinition>();
-			il.Append(DigProperties(properties.Take(properties.Count - 1), locs, null, node as IXmlLineInfo, module));
+			Instruction pop = null;
+			il.Append(DigProperties(properties.Take(properties.Count - 1), locs, () => {
+				if (pop == null)
+					pop = Instruction.Create(Pop);
+
+				return pop;
+			}, node as IXmlLineInfo, module));
 
 			foreach (var loc in locs.Values)
 				setter.Body.Variables.Add(loc);
@@ -681,6 +687,12 @@ namespace Xamarin.Forms.Build.Tasks
 
 				il.Emit(Stloc, loc);
 				il.Emit(Ldloca, loc);
+			} else {
+				if (pop == null)
+					pop = Instruction.Create(Pop);
+
+				il.Emit(Dup);
+				il.Emit(Brfalse, pop);
 			}
 
 			if (lastIndexArg != null) {
@@ -703,6 +715,11 @@ namespace Xamarin.Forms.Build.Tasks
 
 			il.Emit(Ret);
 
+			if (pop != null) {
+				il.Append(pop);
+				il.Emit(Ret);
+			}
+
 			context.Body.Method.DeclaringType.Methods.Add(setter);
 
 //			IL_0024: ldnull
diff --git a/Xamarin.Forms.Xaml.UnitTests/BindingsCompiler.xaml b/Xamarin.Forms.Xaml.UnitTests/BindingsCompiler.xaml
index 3794705..6b5796e 100644
--- a/Xamarin.Forms.Xaml.UnitTests/BindingsCompiler.xaml
+++ b/Xamarin.Forms.Xaml.UnitTests/BindingsCompiler.xaml
@@ -16,6 +16,7 @@
             <Label Text="{Binding I}" x:Name="label5" />
             <Label Text="{Binding Model.Text}" x:Name="label6" x:DataType="local:MockStructViewModel" />
 			<Entry Text="{Binding Text, Mode=TwoWay}" x:Name="entry0"/>
+			<Entry Text="{Binding Model.Text, Mode=TwoWay}" x:Name="entry1" />
             <Label Text="{Binding .}" x:Name="label7" x:DataType="sys:Int32"/>
             <Label Text="{Binding Text, Mode=OneTime}" x:Name="label8" />
 			<Label Text="{Binding StructModel.Text, Mode=TwoWay}" x:Name="label9" />
diff --git a/Xamarin.Forms.Xaml.UnitTests/BindingsCompiler.xaml.cs b/Xamarin.Forms.Xaml.UnitTests/BindingsCompiler.xaml.cs
index b47bdeb..8bdc105 100644
--- a/Xamarin.Forms.Xaml.UnitTests/BindingsCompiler.xaml.cs
+++ b/Xamarin.Forms.Xaml.UnitTests/BindingsCompiler.xaml.cs
@@ -97,6 +97,12 @@ namespace Xamarin.Forms.Xaml.UnitTests
 				Assert.AreEqual("Text2", layout.entry0.Text);
 				((IElementController)layout.entry0).SetValueFromRenderer(Entry.TextProperty, "Text3");
 				Assert.AreEqual("Text3", layout.entry0.Text);
+				Assert.AreEqual("Text3", vm.Text);
+				((IElementController)layout.entry1).SetValueFromRenderer(Entry.TextProperty, "Text4");
+				Assert.AreEqual("Text4", layout.entry1.Text);
+				Assert.AreEqual("Text4", vm.Model.Text);
+				vm.Model = null;
+				layout.entry1.BindingContext = null;
 
 				//testing invalid bindingcontext type
 				layout.BindingContext = new object();
-- 
2.7.4